Implicit Body Representation of the Hand Enlarged by Repetitive Peripheral Magnetic Stimulation within the Boundary of a Real Hand
Round 1
Reviewer 1 Report
- Please provide the quantitative values for the range of stimulation intensity used across participants.
- The paper describes the experimental design in which stimulation was provided to the corresponding skin position of the motor branch of the radial nerve. However, there is no control experiment of the location specificity of the effect was performed. For example, stimulation at a nearby site, etc can be performed to demonstrate the location specificity of the effect.
- Table 2 and 3 includes the results and p-values. In order to avoid false positives, please correct the p-values for multiple comparisons.
Author Response
I wrote them in a word file
Author Response File: 
Author Response.docx
Reviewer 2 Report
First of all, I would like to thank the authors and editors for giving me the opportunity to review this manuscript. I have expertise in the field of motor cognition, neuropsychology of action and body representations. I have no expertise on rPMS methods.
The authors used rPMS on two groups of participants (real vs sham rPMS). The goal of the study was as follows: “we aimed to study whether adding proprioception and static tactile sensation from peripheral body part could induce plastic change in implicit body representation. Therefore, we hypothesized that rPMS applied to the motor branch of radial nerve that induced extensions of the wrist and fingers could increase proprioception input to the corresponding cortex area in the brain, which might enlarge implicit body representation of the hand in return.”. The measures were: “we measured implicit body representation of the non-dominant hand before stimulation, right after stimulation, 10 minutes after stimulation and 20 minutes after stimulation”.
I understood the broad goal and methods of the study. They are relevant to the research field. The theory in the introduction is relevant. I also understand that this is a preliminary study, or a part of a larger project (?) on stroke patients. So, it might be worth publishing. Unfortunately, I have some major comments on the design of the study, the methods and the results section, that prevent me from recommending this manuscript for publication, in its current state. I hope my comments will help the authors improving the manuscript.
MAJOR COMMENTS
I am not a native English speaker so I might be wrong here, but I think the manuscript should be proofread by a native English speaker. For example, the authors rarely use “the” throughout the manuscript ; “is mainly relied on”; “There is a similar research paradigm that movements of the lips could not be guided by vision,”; “Using towel to support the elbow if necessary and record this proper position for use of the following experiment”; “Multivariate showed the within-subject effect of time”…; “here was research demonstrated that”…
Abstract
The abstract does not help to understand the goals, design and conclusions of the study. I think it should be rewritten.
Introduction
The introduction is relatively easy to follow. My main concerns on the introduction are:
(1) The authors describe theories of body representations (body schema, body structural description, body semantics, implicit body reprensentation), but then in the following paragraphs they develop on “body representations” as a broad category. I suggest the authors explain on which body representations they focus here, or at least select a term and stick to it. Indeed, I had difficulties understanding how the authors viewed body representations, because they explained body representation theories quite well, but then they focused on therapies like the constraint induced therapy, that have actually been used for patients with hemiplegia or hemiparesia. Do the authors consider hemiplegia as a body representation deficit? Is there data suggesting a relation between motor deficits on the one hand, and implicit representation of the hand on the other hand? I have difficulties understanding how this paragraph on therapies is useful to understand the experiment.
(2) I think the authors should describe the methods of Longo & Haggard in details (e.g., what participants are asked to do) in the introduction because this would help readers better understand what “implicit representation” means, and because a similar method is used afterwards. Based on the methods, what is called “implicit” representation is actually a “non-visual” body representation. In brief, more explanations here would be useful for readers.
(3) What was exactly the hypothesis behind the suspend vs tactile conditions?
Methods:
The method is in general well written, easy to understand and most of it could be replicated, but in some instances some very important details are missing or not justified:
- Importantly, there are no details on the measures. What was measured exactly?
- Participants: “No statistical differences were found in age and gender between groups”. Please provide the statistics used.
- Why is the rough surface of board B important?
- The participants were recruited in medical school campus. Were they students? If so, were the experimenters/authors teachers of these students?
- It is said that one participant was excluded due to “oversensitive to rPMS”. It is also said (in a sentence that is possibly grammatically incorrect) “Parameters of rPMS machine were set to be 50 Hz, and the maximum intensity of each participant could tolerate (around 70% of the highest intensity of the machine)”. What information did the authors provide to the participants as regards the potential adverse effects, and when?
- Why focusing on the non-dominant hand? Could it have biased the results?
- In the suspend condition, how was the hand suspended in the apparatus? How did the authors ensure that the suspension was totally passive?
- How exactly did the authors control for a possible sequence effect of suspend and tactile conditions? It is said that conditions were randomized and “cross controlled”, what does it mean exactly?
- I do not understand this sentence: “same statistical analysis protocols were run to determine whether there were significant differences in percentage of perceived lengths compared to real lengths”.
- Statistics: the authors used ANOVAS and controlled for variance using Mauchley’s test and Greenhouse-Geisser correction. Did the authors control for other parameters that are critical to apply parametric statistics like ANOVAs? In other words, were the measures normally distributed? If not (which is likely with small samples of 20 participants), non-parametric tests would be preferable. Also, there have been a lot of comparisons, was p value corrected for multiple comparisons?
Results
- Since there is no effect of suspend vs tactile conditions (as I understand it), and since it is not part of the hypotheses, I do not understand this part of the design.
- I do not understand Table 2 as the latter displays “percentages of perceived lengths”..? Since the measure is not explained in the methods, it is not easy to understand. I can only guess it but please, provide details.
- There are too many measures and analyses, as shown in the tables. I would recommend averaging suspend and touch measures since there is no difference (?). I also recommend focusing the analyses on the perceived vs real differences (table 2) as this is the only measure that informs us on “implicit body representation”, which is the main topic of the study. I also recommend averaging scores for each finger, unless there is a reason not to. Finally, these changes would result in a single table with two rows (Wrist, Fingers), and in columns only the Real/Sham rPMS and time variables (If this variable is relevant to the goal or method, which I feel is not the case). If the effect of rPMS is robust, it will probably resist these changes and the study will be easier to understand, in my opinion.
- That said, I have some doubts because in table 2, where p values are below .05, there is actually no clear difference between sham and real. For example, for PP4, right after the stimulation, for tactile condition, sham=70.3 (sd 14.8) and real=65.2 (sd 13.2). Based on data observation, given the standard deviations, the significant p-values could be artifacts… I think the authors should reduce the number of measures (see above), and make clear the comparisons they made and the corresponding p-values. Perhaps the authors could focus on sham vs real comparisons right after the stimulation (which is actually the main point the study tries to make, as I understand it) in a table, then on the effect of time in secondary analyses – again, only if relevant for any demonstration.
- I would recommend providing the findings in a figure like scheme 2 but with the average position of the estimated point of each finger and wrist, if possible. This would help better understand the conclusion that the estimation remains within the boundaries of the hand.
Discussion
I do not review the discussion in details because I think the abovementioned concerns should be addressed to verify how they change the findings. Some important comments though:
- The authors conclude: “our hypothesis was partially validated that adding proprioception input contributed to the enlargement of implicit body representation of the hand.”. I think that strictly speaking, this is an overinterpretation because the authors did not “add proprioception”, they stimulated some nerves. Whether the observed effect is linked to this stimulation, is an interpretation.
- The authors discuss the fact that the estimation remains within the boundaries of the real hand, but since this had not been developed in the introduction, the reader cannot understand why it is important. Also, if this is important, the results section should be designed to emphasize it.
- In the discussion the authors do not discuss the time variable (0, 10, 20 minutes) so I still do not understand how this variable was relevant to the study and research field.
MINOR COMMENTS
I have concerns regarding the structuration of the introduction. The first paragraphs focus on body representations, then implicit body representations, then on rPMS, then back on implicit body representations. I would suggest writing one paragraph on body representations with all the information needed, before shifting to rPMS and then the goals of the study. It would be easier to follow, I think.
I think the manuscript should be checked for typos. For example: “are integrated and processed faster comparing to the surrounding object of a similar complexity” à Compared to, objectS.
L57: the following formulation “the brain progressively suppresses the use of the affected extremity” sounds odd to me, as the brain does not “use” anything. Do the authors refer to the reorganization of somatotopic brain maps here?
L62: I do not understand the expression “a closed loop of recovery” the way it is written. I do not think this is essential to the manuscript.
L69: “Even pilot study on the plastic change of body representations in health is insufficient neither.”. I did not understand what the authors referred to, in the absence of reference. It could be removed.
In table 2, lines are “PP” but the caption says “PL”.
I think the paragraph on goggles in the discussion is not essential to this manuscript.
Author Response
I wrote them in a word file
Author Response File: Author Response.docx
Reviewer 3 Report
I found the paper and the topic interesting, I have no correction to suggest.
Author Response
I wrote them in a word file
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
My comments during the previous review have been addressed by the authors. There are no further suggestions.
